Bombesin represents one class of neuropeptides active in the mammalian central nervous system and gastrointestinal tract. Endogenous bombesin-like peptides have been identified in these systems by radioimmunoassay and by immunocytochemistry. The bombesin-like peptides are localized to synaptosomes and thus may function as physiologically important neurotransmitters. The overall objective of this proposal is to investigate the biological function of bombesin-like peptides and the receptors with which they interact in mammalian brain. The regional distribution of bombesiun-like peptides will be determined using a radioimmunoassay combined with microdissection techniques. In parallel, the regional distribution of receptors which interact with these peptides will be examined using autoradiography techniques. The mechanism of release of endogenous bombesin-like peptides will be investigated using rat brain slices. Finally, the structure of bombesin-like peptides extracted from porcine brain will be determined using biochemical techniques.